feat(bot): add trace log for LLM prompt in BotOrchestrator

Added a trace-level log statement to output the constructed LLM prompt in BotOrchestrator. This helps with debugging by making the prompt content visible in logs when trace logging is enabled. The change maintains existing functionality while improving observability.

src/bot/mod.rs

@@ -444,7 +444,7 @@ impl BotOrchestrator {
             "Stream prompt constructed with {} history entries",
             history.len()
         );
-
+        trace!("LLM prompt: [{}]", prompt);
         let (stream_tx, mut stream_rx) = mpsc::channel::<String>(100);
         let llm = self.state.llm_provider.clone();